Mechanical Behavior during Electrochemical and Mechanical Deactivation of an Aged Electrode in a Lithium‐Ion Pouch Cell

Abstract

The mechanical behavior of lithium‐ion battery electrodes that undergo a severe capacity decrease are investigated by monitoring the out‐of‐plane displacement on the external surface of a pouch cell. The capacity degradation does not decrease gradually as a function of time but exhibits distinct behaviors with different causes. These are electrochemical aging during cycling and mechanical injury caused by manufacture failure. In the former case, both the permanent evolution and the anomalous distribution of the displacement accompanied with a consistent decrease of the capacity are correlated to the local deterioration of the adhesion of the material layers. The mechanical injury accelerates the capacity decrease by destroying the electrode structure, which results in a sudden decrease of the surface displacement. If the displacement reaches its limit, only a dynamic fluctuation remains, which reflects the remaining electrochemical process at a low level. As a result, we conclude that the loss of electrical connectivity between the active material layer and the current collector is responsible for the severe capacity degradation. This effect is more pronounced on the anode than the cathode. Both electrochemical cycling and mechanical injury can result in the weakening of the adhesion of the anode material on the current collector.

Surface and Electrochemical Studies on Silicon Diphosphide as Easy-to-Handle Anode Material for Lithium-Based Batteries—the Phosphorus Path

“…Moreover, the signal at −190 ppm is attributed to LiP formation, which was often found during the cycling of phosphides, such as Sn 4 P 3 or CoP 3 . , Discharging to a lower voltage of about 0.5 V (A2, red) results in further amorphization of SiP 2 without a crystallization of Li 3 P nanoparticles, as shown by XRD. The reduction peak at 350 mV is observed according to the incipient formation of crystalline Li 3 P, which is completed around 0.1 V versus Li/Li + (Figure , A2*, gray) and correspond to the 31 P NMR signal at −280 ppm, as reported in the literature. , The small drop in the range of 0.01 V ≤ E ≤ 0.1 V, more pronounced and better visible in Figure , might be interpreted as the formation of a lithium silicide phase, which can typically occur below 0.1 V versus Li/Li + 11 and is taken as an indicator for the successful formation of amorphous Li x Si . Crystalline Li 15 Si 4 , the highest lithiated phase of silicon, cannot be observed by XRD (Figure b) even at 10 mV, only confirming the formation of amorphous Li x Si.…”

“…20,45 The small drop in the range of 0.01 V ≤ E ≤ 0.1 V, more pronounced and better visible in Figure 6, might be interpreted as the formation of a lithium silicide phase, which can typically occur below 0.1 V versus Li/Li + 11 and is taken as an indicator for the successful formation of amorphous Li x Si. 9 Crystalline Li 15 Si 4 , the highest lithiated phase of silicon, cannot be observed by XRD (Figure 7b) even at 10 mV, only confirming the formation of amorphous Li x Si. Finally, at 10 mV versus Li/Li + (A3, blue), crystalline Li 3 P is visible as evidenced by NMR and crystallizes with an average crystallite size of about 80 nm in a structure type with the hexagonal space group P6 3 / mmc and the lattice parameters a = 4.3483(1) Å and c = 7.7168(2) Å which exhibits a layered structure of alternating Li 2 P and Li layers.…”

“…This action increases the loss of electrical contact and leads to a high electrolyte consumption and, thereby, rapid capacity fading. (III) Displacement of a part of the anode composite during cycling additionally increases the contact loss problem. ,− One possibility to overcome this problem is to nanostructure the sample. ,,, Therefore, silicon nanoarchitectures such as silicon nanowires, − nanopillars, , thin films, and nanoparticles ,, have been tested.…”

Comparison of fresh and aged lithium iron phosphate cathodes using a tailored electrochemical strain microscopy technique

“…Therefore, the presented ESM measurements visualize the reduction of the electrochemical activity and the loss of lithium inventory of the sample due to ageing on the nanometer scale. With that, ESM offers a higher resolution technique for the visualization of the activity compared to digital volume correlation [47,48] and digital image correlation [49], which have a resolution of 2 µm or more.…”